Car just had all the seals rear, main and transmission replaced about 2-3 weeks ago. It was leaking oil.

The car has ran fine without any issues thus far until last night. I was driving as I normally do nothing out of the ordinary maybe going a bit slower than usual because of traffic and the car sputtered just for a second and went away. So I didn’t read much into it until about 10-15 minutes later I was going about 10mph and the car died. All the lights came on just as it does when on accessory 2 along with the check engine light. Luckily I was able to park the car out of the way. So without even turning off the car I put it in park and attempted to start it but it wouldn’t start just act like it wanted to but nothing. So I turned it off and opened the hood to see if I could see anything out of the ordinary and I didn’t and got back in the car and started it up without issue. So I put it in reverse and attempted to back out of the position I was in and then put it in park and attempted to move when it started sputtering again and wanting to stall. I decided at this point to leave it and walk to my destination, which was about a mile a way. When I got back to the car about 2.5 hours later it started without issue again but when I put it in drive and gave it gas it started sputtering again and stalled so I attempted to start the car by putting it in neutral and cranking the engine, This did not start the car (BTW the car is coasting on the road at this point) so while it was still in neutral I moved the key back to accessory 1 and the car started back up without hesitation. But when I applied gas it wanted to stall and sputter but somehow I kept it going and was able to get up to 50mph and stayed there pretty consistently while driving home. While I was driving the car did sort of hesitate and seem like it wanted to stall sputter and die again but didn’t until I got closer to home and had to slow down. When it stalled on me I did the same thing where I put it in neutral and moved the key to accessory 1 and the car started without a problem but wanted to stall again when accelerating trying to get home. Finally got the car home and called my brother-in-law who is a mechanic to see if I could get him to look at it.

He came out the next day and connected his work scanner to the car and received and error code of P0336. So he checked a couple of things on the car and said all looked ok. (BTW he was the one who replaced all the seals on the car) So we took the car for a spin around the block. And once again the car started without issue. We got about ¾ of a mile around the block and the car started doing its thing. I would apply the gas petal and it would want to stall and sputter. On this trip we noticed several things. 1- the car did not want to go any further than 3000 RPM no matter how much gas I applied. 2- the electrical reading on the car with the code checker still attached was reading 12v and seemed to be running off the batter only but then would go away. So we got back home and did some more testing and found out still after resetting the codes that when the car stalled in accessory 2 the key still needed to be put back to accessory 1 before it would start. He also connected a spark plug tester thing (sorry not sure about the name, one end went into the spark plug well and the other end went into the spark plug wire and there was a flashing light in the middle. He said that this was good. We also tested the alternator with a voltmeter and it seemed ok. Then we got in the car and started the car again and this time turned all kinds of stuff on A/C, radio, turn signal, high beams and placed the car in park and all seemed ok at about a 1000RPM but when we turned off the A/C the car tried to sputter again. We have checked the fuel pump and ignition switch and they OK. The car just wants to stutter and die when gas is applied even while in park. Any suggestions or help would be appreciated on this. He is concerned of a false positive on the error codes and does not want to throw parts at it to fix it.

I picked out a few useful clues and observations and it sounds like there's two things to consider. The first is a plugged pickup screen in the gas tank. That will prevent sufficient fuel from getting through. They often collapse after driving a little ways, then stretch back out when the engine is off. Connecting a fuel pressure gauge should show a severe loss of pressure when the problem occurs.

The next thing is the generator. You mentioned some voltage going down to 12 volts. The charging system voltage must remain between 13.75 and 14.75 volts with the engine running. Besides that, it must be able to deliver sufficient current to run all the electrical systems plus recharge the battery. When one of the six internal diodes is defective, you will lose exactly two thirds of the output capacity. The common 90 amps generator will only be able to supply about 30 amps which is not sufficient to run the electric fuel pump, fuel injection, ignition, and other computers and circuits. When the capacity can meet the demand, the system voltage will still be high enough, and sometimes a little too high, (above 14.75 volts). That is a clue but the definitive test is to have a load test performed on the generator.

Also, when one diode is bad, "ripple" will be very high. I can explain that further if you want me to. Basically it means the system voltage will be varying a lot and very rapidly. You might also hear a louder than normal whine on an AM radio station that changes in pitch with changes in engine speed. That ripple wreaks havoc on computers because they are not tolerant of voltage fluctuations or low system voltage. Bad diodes are often responsible for computers doing weird things that defy most troubleshooting procedures.

So I checked the wiring and all seems OK. No loose connections and also disconnected several connectors and reconnected to cover the bases.

I connected a volt meter to the car while it was running and it read 14.6 while the car was running (about 2 minutes) and revving the engine. The car stayed on the entire time. So I let the car sit and idle for about 20 minutes and retook the volt test and the car was at 14.5. Turned on the A/C and head lights (High beam) and the volt reading dropped to 14.2. So I revved the car up again and within about 30 seconds of doing that the car died again and the reading dropped to 12.7 immediately from 14.2. Went back about 2 minutes later and took battery reading and it is at 13.2

If I understand correctly, you measured the voltage at the battery and it dropped to 12.7 volts AFTER the engine died. If I have that right, that is normal and correct. 12.6 volts indicates a fully charged battery. Dropping to 14.2 volts when many accessories are turned on may be a clue. While that is within the acceptable range, it suggests the generator isn't keeping up with demand, however, all generators lose efficiency at lower speeds. If you find the voltage comes back up when you increase engine speed a little, that is normal.

That still doesn't address the load test though. That must be done with a professional load tester. Most of them also display ripple, not as a voltage, but as a relative bar graph. High ripple is indicative of a bad diode.

Dandy. I hope they tested it for maximum output and ripple. I never took a generator in for testing so I don't know what they look for. I've been told some places just check to see if it can produce some output. That's not nearly good enough. All of my testing is done with a professional load tester with the generator on the car. It must be able to deliver its rated current when engine speed is raised to 2000 rpm. I've never seen a bench tester that can run a generator that fast.

If a professional load test shows low ripple, and maximum output current can be produced, I'd start by monitoring fuel pressure. I like to hook the pressure gauge under a wiper arm so I can watch it while I'm driving. You'll get used to seeing how the pressure changes when you're on and off the gas, then you'll notice it if it acts differently when the problem occurs.